This invention relates to gelling agents, gels and to processes for preparing them. It also relates to products comprising the gels, in particular matrices for delivering active agent and food products.
Gels are formed from macromolecular hydrocolloids and have the ability to form non-deformable structures with low impact resistance. The classical gelling agent, which has been most widely studied, is gelatine. This is also the only known food grade hydrocolloid which is a protein. Gelatine is, nutritionally, a low quality protein and gels incorporating it have the disadvantages that they tend to harden on storage and may develop undesirable textural properties. Gelatine may also have negative religious and/or health connotations for some consumers, as it is produced in a manner destructive of animals and there may also be concerns arising from a perceived link with Transmissible Spongiform Encephalopathies such as Bovine Spongiforms Encephalopathy or Creutzfeld-Jacob Disease
It is an object of the present invention to provide a gelling agent which will go some way towards overcoming the above disadvantages, or at least to provide the public with a useful choice.
In a first aspect the present invention may broadly be said to consist in a gelling agent which comprises modified casein, the native structure of the casein having been disrupted sufficiently to cause a composition to which the casein is added in use to gel.
Preferably, the gelling agent comprises a dispersion of modified casein in water and a suitable plasticiser, preferably glycerol.
In a further aspect the present invention provides a method of preparing a gelling agent which comprises the steps of:
(a) forming a dispersion comprising casein and water; and
(b) heating the dispersion for a sufficient time and to a sufficient temperature to disrupt the native structure of the casein.
In another aspect the present invention may broadly be said to consist in a process of preparing a gelled product which comprises adding a gelling agent as defined above to a gellable composition.
In yet a further aspect the invention may broadly be said to consist in a process of preparing a gelled product which involves the use of casein as a gelling agent.
In still a further aspect the present invention may broadly be said to consist in a gelled product which includes a gelling agent as defined above.
In preferred embodiments, the gelled product is a food product.
In other alternative preferred embodiments, the gelled product is a delivery matrix which comprises (a) a matrix which includes the modified casein; and (b) an active agent incorporated in the matrix.
In yet a further aspect the present invention may broadly be said to consist in a method of preparing a gelled product which comprises the following steps:
(a) forming a dispersion comprising casein and water;
(b) heating the dispersion for a sufficient time and to a sufficient temperature to disrupt the native structure of the casein; and
(c) removing the source of heat, adding other gellable components and allowing the resulting mixture to set into a gel.
Preferably, the dispersion also comprises a plasticiser (preferably glycerol) and a suitable buffer to maintain the pH in the range of about 6.1 to about 10.10.
As outlined above, the invention relates generally to gelled products and to macromolecular gelling agents used in their preparation.
The ability of a macromolecule to gel depends on interaction between molecules at restricted points along the macromolecule. Portions of the molecule that do not interact disperse in the continuous phase (usually water). Energy is usually required to disrupt the native structures of hydrocolloids. For instance, gelatine is manufactured by applying heat to collagen. The applicants have discovered that the native structure of casein can be disrupted sufficiently for gel formation. This can be achieved, for example, by heating, generally to a temperature of about 95-110xc2x0 C. or above. It is this finding by the applicants which forms the basis for the present invention.
In a first aspect, the invention provides a gelling agent which comprises modified casein, in which the native structure of the casein has been disrupted sufficiently to cause a composition to which the casein is added to gel. The gelling agent preferably comprises a dispersion of the modified casein in a suitable plasticiser (preferably glycerol or glycerol combined with propylene glycol (1,2-propanediol) and water, although other forms of the modified casein are by no means excluded.
The gelling agents of the present invention have a number of potential applications. For example, in some embodiments of the invention, the gelling agents may be used in food products. In other embodiments the gelling agents may be used in preparing non-edible gels. For example, they may form part of a delivery matrix in which a matrix containing the modified casein encapsulates an active agent.
The preferred formulation of a particular gelling agent of the present invention will depend on the desired end use of the gel.
For example, alteration of the amount of plasticiser, if any present will change the characteristics of the resultant gel. Similar changes can be effected by changing the identity of the plasticiser. By way of illustration, using 1,2-propanediol as a plasticiser instead of, or partially instead of glycerol, results in a softer gel with a lower melting point. This may be desirable for some applications, for example where volatiles are to be entrapped or encapsulated by the gel matrix.
It is also possible to produce a lower melting point gel matrix through the addition of excess water during formation of the matrix. The excess water can then be removed again after the volatiles are encapsulated by gently drying over silica.
A still further approach to modifying the properties of the gel matrix is to replace a small amount of modified casein with gelatine (between 10% and 20%). This produces a lower melting point gel matrix which is softer than the equivalent matrix using casein alone.
Various embodiments of the invention are described in more detail below.
Food/Confectionery Applications
As noted above, in some preferred embodiments the gelling agents of the invention are used in preparing food products. In these embodiments, the gelling agents, and gelled products containing them, may be prepared by first forming a dispersion comprising water and preferably an edible plasticiser, most preferably glycerol, with the dispersion having a pH in the range of about 6.1 to about 8.0. It is preferred that the pH is about 7.5. It is generally desirable that the pH be within the above range when the gelling agent is to be incorporated into a food product, as the resulting gel may be waxy and brittle if the pH is lower than this, or may be unpalatable if the pH is above the upper limit of the range.
Suitable buffers to achieve this pH will be apparent to those skilled in the art. However, a preferred buffer is a combination of sodium citrate, calcium carbonate and sodium carbonate. It is preferred that the sodium citrate is present in an amount of about 1.0% to 2.0%, more preferably about 2.0%, by weight of the resulting gel, that the sodium carbonate is present in an amount of about 0.2% to 0.8%, more preferably about 0.4%, by weight of the gel, and that the calcium carbonate is present in an amount of about 0.4% to 1.0%, more preferably about 0.8% by weight of the gel.
It should also be noted that the calcium carbonate, as well as acting as a buffer, acts as a texture modifier, resulting in a gel with a firmer texture, which is desirable when the gel is to be used as a confectionery product such as a wine gum. The firmer texture is believed to result from interaction between the calcium ion and the casein.
In one preferred embodiment of the invention, glycerol is present in an amount of about 40% to about 55% by weight of the gelled product. Glycerol is a humectant and acts as a plasticiser in the gel. Thus, the more glycerol present, the softer the gel. The above range of glycerol concentrations has been found to be desirable for preparing gelled food products having a texture suitable for confectionery products such as wine gums. Of course, for other applications, a harder or softer gel may be desirable and the glycerol concentration should be adjusted accordingly.
The water acts to disperse the buffer. In the preferred embodiment of the invention mentioned above, in which the gelled product is suitable for use as a winegum type product, sufficient water is added so that water is present in an amount of about 26.7% to 34.6% by weight of the gel, more preferably about 30.2% by weight.
It is also preferred that the casein is washed before use in order to remove low molecular weight material. The presence of such low molecular weight material may result in the product having a bitter aftertaste. A suitable method of washing the casein is to use distilled water, preferably at a ratio of about 20:1 water:casein. The water and the casein are mixed together, and the mixture stirred for approximately one hour, the temperature then increased slowly to 30 C. and held for approximately 30 minutes. The mixture is then put on ice, stirred for a further two hours and the small molecular weight casein is removed by filtration, that is, it remains in the filtrate. Other suitable methods of washing the casein will be apparent to those skilled in the art.
The amount of water present significantly influences the texture of the gelxe2x80x94if too much water is added the resulting gel may be unacceptably soft for a particular application, whereas too little water will result in a gel which is too hard. Again, the amount of water added will need to be adjusted for the particular application to which the gelling agent is to be put.
The mixture of the buffer, glycerol and water is then preferably heated to about 40 C., and stirred until the buffer is dispersed. Once the buffer has been dispersed, casein is added to the mixture. The casein should be added sufficiently slowly to avoid the formation of lumps. In the preferred embodiment described above, the proportion of casein in the gel is about 18% by weight. Concentrations of casein significantly lower than this may produce gels which are too soft and fail to hold their shape after gelling, whereas significantly higher concentrations may produce gels which are too hard and do not have the xe2x80x98gummyxe2x80x99 texture required when the product is to be a confectionery product such as a wine gum. It will of course be appreciated that gels which are either soft or hard will be appropriate for applications other than as a confectionery such as a wine gum. Gels which contain more or less than 18% by weight of modified casein are therefore in no way excluded from the present invention.
It should be noted that, if, as is preferred, the casein is washed, the washed casein will retain a significant amount of water. This means that the water content of the casein will need to be determined and the amounts of water and casein adjusted accordingly, to give the desired proportions of water and casein in the composition.
After the casein has been added, the mixture should continue to be stirred. In addition, the mixture is heated to a sufficient temperature and for a sufficient time to disrupt the native structure of the casein sufficiently to allow gel formation to occur. It is preferred that the mixture be heated until the temperature reaches about 100 C., more preferably about 112 C., or when foaming lessens. The heating time required will depend on the rate of heating, but in practice, a heating time of between about 6 and 13 minutes will usually be sufficient.
The resulting solution, which is the gelling agent, is then removed from the heat. When the gelled product is to be a winegum-type confectionery, it is also preferred that additional components are then added to the solution. These preferred additional components are:
(1) a sweetening agent. A preferred sweetening agent is a combination of fructose and aspartame. However, alternative sweetening agents (both nutritive and non-nutritive) will be known to persons skilled in the art, and may also be used. A concentration of fructose of about 6.0% to about 10.0% by weight of the gel, most preferably about 8.0% by weight, and aspartame, in an amount of about 0.1% by weight of the gel have been found to produce an acceptable level of sweetness. However, the amounts of the sweetening agents may of course be adjusted depending on the desired level of sweetness in the gel.
(2) a flavor modifier which reduces bitterness. As the casein molecule suffers significant damage during heating, the resultant gel may have a bitter aftertaste. The use of a suitable flavor modifier will eliminate this. In the preferred embodiment, the flavor modifier is maltol (3-hydroxy-2-methyl-4-pyrone), present in an amount of about 0.1% by weight of the gel. Maltol minimizes bitterness and enhances sweetness.
(3) a texture modifier. A particularly preferred texture modifier which has been found to improve the texture of the gel is carrageenan, which is preferably added in an amount of about 0.15% to about 0.25% by weight of the gel. It will be appreciated by persons skilled in the art that alternative texture modifiers, for example gums such as carboxy methyl cellulose, may also be used.
Components (1) to (3) are stirred into the solution after it has been removed from the heat, until all components have been dispersed. If desired, food grade colorings and/or flavorings may then also be added.
The resulting mixture is then allowed to cool and set. It is preferred that the mixture be poured into a mould so that the gel sets in a desired shape. When the gelled product is to be a winegum-type confectionery, if desired, the gelled product can be coated with an agent which hardens the outside of the gel. If such a coating is desired, then approximately one hour after pouring, the gelled product can be removed from the mould and coated with the hardening agent. A preferred hardening agent is a citric acid/calcium citrate dip, consisting of an aqueous solution comprising about 15% by weight citric acid and 1% by weight calcium citrate. The pH of the dip is preferably about 2.0, which is lower than the isoelectric point of casein (pH 4.5).